1. Field of the Invention
The present invention relates generally to the art of finishing workpieces by using rotary barrels, and more particularly to a method whereby a centrifugal force is produced within those rotary barrels, thereby providing for improved workpiece finishing efficiency and uniformity.
2. Description of the Prior Art
A conventional workpiece finishing method of the class disclosed herein consists of using a rotary barrel having the polygonally-formed container having multiple sides which contains workpieces to be surfacefinished or otherwise processed as well as the abrasive media including a compound solution (the mixture of which will be referred to collectively as a "mass"), and causing the rotary barrel to rotate on its axis. the axial rotation of the rotary barrel in this manner produces a centrifugal force which causes the workpiecees and abrasive media to interact against each other. When the barrel is rotating with the proper number of revolutions, the mass within the barrel can have a flow layer formed above it. Thus, the smooth finishing process can occur. With the increasing number of revolutions, however, the mass may flow in a disorderly fashion which may cause the mass to lose its ability to flow smoothly. This may have the accompanying effect of letting part or all of the mass to fall or follow the projectile motion. Thus, the finishing process cannot occur properly. When the number of revolutions is increased further, a centrifugal force may be produced, bringing all the mass closer to the inner barrel wall and forcing it against the wall. Finally and eventually, the mass remains motionless. In that condition, it would be practically impossible to continue the processing. When the mass has the behavior or motions as described above within the polygonally-formed container, the relationships between the diameter d (m) of an inscribed circle across the polygonal shape and the number of revolutions n (rmp) have been defined. According to this definition, the optimum running requirements can be met when n=14/.sqroot.d, the maximum amount of work can be achieved when n=32/.sqroot.d, and for n-42.2.sqroot.d, the mass may be forced against the barrel wall under the action of the produced centrifugal force. According to the conventional finishing process, therefore, it has been observed that when the number of revolutions n is greater than 14/.sqroot.d, the resulting performance may be degraded rather than being improved. There are various types of abrasive media and compounds available for use with the various types of workpieces and they have been improved to allow for the further increased number of revolutions n. Still, the maximum possible number of rovolutions is limited to n=20/.sqroot.d, and any value beyond this maximum would adversely affect the finishing efficiency. For this reason, the conventional finishing method as described above can only be used within the value of n=20/.sqroot.d.
Another conventional finishing method is known, which consists of using a high-speed revolving barrel and causing a centrifugal force to be produced within the barrel, within which the mass can flow under the influence of the produced centrifugal force. This method provides the enhanced finishing efficiency. When the mass is placed under the influence of the centrifugal force, it is forced against the barrel wall as described earlier. In order to prevent this situation, the second-mentioned conventional method employs the conceptual principle of operation whereby a barrel is mounted to a high-speed turret so that the former can rotate with the latter in an eccentric relationship with regard to the latter. When the turret is rotating with a given number of rovolutions N per minute, the mass within the barrel is also subjected to the produced centrifugal force which brings the mass closer to the barrel wall. To overcome the action of the centrifugal force, the barrel which is supported on its own shaft is also driven for axial rotation with a given number of revolutions n per minute. If the ratio of n/N has a certain value, a flow layer is formed on the surface of the mass, and a good result is obtained. It is known that when n/N=-1, which means that the turret and barrel are rotating in the opposite directions with the same number of revolutions, the best result may be obtained. The definition of the centrifugal barrel is determined that the centrifugal force produced by rotating the turret exceeds the limit that the mass is compacted against the barrel wall if there is no rotation about the barrel axis. The upper limit for N is defined as N=42.2/.sqroot.D (where D is equal to two times the distance between the center axis of the barrel and the center axis of the turret, in meters). In those years, the needs for the barrel finishing technology that allows for the very high-precision and very high-speed finishing process have been increasing as the increasing number of a variety of electronic components or parts using ceramics or fragile materials have been developed and used. In order to meet those needs, the centrifugal barrel finishing method has been used. In some cases, however, there may be problems of producing too strong centrifugal force during the operation, or causing a disorderly flow of the mass at the start or end of the operation. In either case, the finished surface may be injured. For this reason, an alternative solution must be provided that could meet the requirements for high precision and strainless workpiece finishing. It is said that the rotary barrel finishing method provides the equivalent capabilities of the very high-precision finishing and lapping when it is used under the adequate conditions, and the corresponding results can be obtained therefrom. It is also noticed that the finishing speed that can be attained by that method is very slow. More specifically, the conventional rotary barrel finishing method consists of producing a centrifugal force which in turn produces a greater resultant force upon the mass during the finishing process, thereby increasing the finishing speed with which the high-precision barrel finishing process can occur. As a possible alternative solution whereby the finishing speed may be increased by increasing the number of revolutions for the barrel above n=20/.sqroot.D, the shaft supporting the barrel may be eccentric with regard to the turret shaft, and the turret may be rotated with the reduced number of revolutions while the barrel may be rotated on its shaft, as it is done for the centrifugal flow barrel. When this proposed solution is used with the conventional centrifugal barrel supported by its horizontal shaft, the magnitude of the centrifugal force that is produced may vary as the barrel is rotating around the turret, changing its orbital position, as shown in FIG. 1 (which is provided for the centrifugal force of IG, in which it is shown that for n/N=-1, the acceleration produced by the centrifugal force has a value equal to that for the acceleration by the gravity. This condition will be referred to hereinafter as simply to the centrifugal force G, or xG when the acceleration by the centrifugal force is equal to x times the acceleration by the gravity). Thus, the magnitude of the force that is applied to the mass may vary during a complete revolution of the barrel, causing a disorderly flow of the mass. It may be appreciated that this may adversely affect the finishing efficiency. When that propoed solution is used with the centrifugal flow barrel supported by its vertical shaft, the resultant centrifugal force that is produced during the complete revolution has the same magnitude, as opposed to the horizontal shaft barrel, but the mass flow may have its surface inclined. Thus, the smooth mass flow cannot be obtained. As the mass contains workpieces of different specific gravity, the workpieces may be separated, depending upon the different specific gravities. Those workpieces which have a greater specific gravity may fall down, gathering together on or near the bottom. This may produce damages to those workpieces by causing them to strike against each other.